1. Field of the Invention
The invention relates in general to a memory, and more particularly to a memory capable of reducing sense window loss of sense currents due to temperature effect on threshold voltage of memory cells. The memory cells are the two-bit Nitride-based trapping storage flash cells
2. Description of the Related Art
Non-volatile memory, such as flash memory, is widely used in various electronic products. Referring to FIG. 1, an illustration of a programmed threshold voltages distributions of a memory is shown. For example, the flash memory is a memory with multiple level cells (MLCS), which can be programmed to have four threshold voltage distributions shown as curves d1-d4 corresponding to two bits of data stored in each of the MLC. In a read operation of a selected MLC, the selected MLC has to be read with three different word line voltages to obtain three cell currents accordingly. For example, the three different word line voltages have the respective levels V1, V2, and V3. The three cell currents will be compared with a reference current, so as to obtain the data stored in the MLC.
In real cases, the threshold voltages of MLCS will be varied due to temperature effect. To be more specific, the MLCS will suffer from descents of threshold voltage when the surrounding temperature is raised and the amounts of descents are proportional to the levels of the threshold voltage. For example, the four threshold voltage distributions of MLCS in the memory can be shown as curves d1′-d4′. Thus, MLCS in the memory will suffer from read window loss due to the raised threshold voltages of the MLCS when the surrounding temperature is raised.